There are various applications in which it is necessary to move a specific member very rapidly and with a high degree of precision into a selected one of a number of different predetermined positions, i.e. to perform stepping of that member. Such positioning is required, for example, for the magnetic head of a multi-track magnetic tape recorder or a magnetic disk drive unit, such as are widely used in the data processing fields. This positioning is carried out in order to align a part of the magnetic head with a desired track of the magnetic medium. In the prior art, such stepping positioning has been performed by means of a motor, which drives the member to be positioned through coupling means such as a cam or drive screw. With such prior art stepping means, since track positions on the magnetic medium are selected by directly driving the magnetic head from a motor, then in order to attain the necessary high degree of precision in positioning the magnetic head, this motor must have a substantially higher drive power capability than is necessary simply to move the magnetic head and furthermore in the case of a stepping motor being employed, it must generally also have a high degree of shaft positioning accuracy. Thus, the motor of such a prior art position determining mechanism for a magnetic head must be relatively large and heavy, and due to the positioning accuracy requirement it must also be relatively expensive. This has been a considerable obstacle hitherto in efforts to make such a position determining mechanism for a magnetic head more compact, lightweight and inexpensive than has been possible in the prior art.
The present invention has the objective of overcoming the problems of the prior art described above. With a position determining mechanism for a magnetic head according to the present invention, positioning of a magnetic head is performed by using a stepped disk, i.e. a disk having a plurality of steps of different thickness formed thereon, with the disk being coupled to the magnetic head in such a way that the current position of the magnetic head is determined by the thickness of a corresponding one of these steps on the disk, previously selected by rotation of the disk, as described hereinafter. With such a method, the positioning accuracy of the magnetic head is determined solely by the dimensional accuracy of the steps on the disk, i.e. the accuracy of the thickness of each of these steps. The motor which rotates the stepped disk does not directly move the magnetic head itself, so that this motor can be small and light in weight, with low power consumption. In addition, the stepping accuracy required for this motor is extremely low, so that a simple and inexpensive motor can be employed, thereby substantially reducing the overall cost of a position determining mechanism for a magnetic head according to the present invention by comparison with the prior art.